Explain why the Integral Test can or cannot be used to determine whether each series is convergent. You do not have to determine if the series converges or diverges.

$($a$){\displaystyle \underset{n=1}{\overset{}{}}}\frac{cos(n)}{\sqrt[\phantom{2}]{n}}$

$($b$){\displaystyle \underset{n=1}{\overset{}{}}}\frac{co{s}^2(n)}{1n^2}$

$($c$){\displaystyle \underset{k=1}{\overset{}{}}}\frac{1}{(3k-1{)}^4}$